Magnetically focussed beam electron discharge tube



Jan. 30, 1968 E. G. .DORGELO ETAL 3,366,823

MAGNETICALLY FOCUSSED BEAM ELECTRON DISCHARGE TUBE v I 2 Sheets-Sheet 1 v H6. c041 ECTO R (AA Filed March 15, 1966 f J 1 \EMITTER(CATHODQY F/GZc /-'/6.2e g 8 O H FIG-2g N 0612/1 F/G. Za

HEIGHT WIDTH w INVENTORS EDUARD a. DORGELO CULLECTOR 502F465 BERTRAM GREEN JOHN E. FINN E'NT FIG. 4

BEAM

'Jan. 30, 1968 E. G. DORGELO ETAL 3,366,823

v MAGNETICALLY FOCUSSED BEAM ELECTRON DISCHARGE TUBE 2 Sheets-Sheet 2 s w m 0. E I- T E N6 A Wm W W. a v a GM 6 MAMHF 6 Wm EH E 5w Filed March 15, 1966 United States Patent 3,366,823 MAGNETICALLY FOCUSSED BEAM ELECTRON DISCHARGE TUBE Eduard G. Dorgelo, Huntington, Bertram Green, Hicksville, and John E. Finn, Plainview, N.Y., assignors to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Continuation-impart of application Ser. No. 452,063,

Apr. 30, 1965, which is a continuation-impart of application Ser. No. 385,259, July 27, 1964. This application Mar. 15, 1966, Ser. No. 534,308

9 Claims. (Cl. 313162) ABSTRACT OF THE DISCLOSURE An electron discharge tube employing magnetic focussing of the electron stream between the cathode and anode, and a gate between the cathode and electrode providing a transverse electric field for controlling the electron flow without substantially intercepting any electrons.

This application is a continuation-in-part of application Ser. No. 452,063, filed Apr. 30, 1965 which is a continuation-in-part of application Ser. No. 385,259, filed July 27, 1964.

The invention relates to an electron discharge tube employing magnetic focussing of the electron stream between the cathode and anode.

As pointed out in the previous applications, the usual limiting factor in the operation of a grid-controlled electron discharge tube is the amount of power which can be dissipated by the gridand this is usually quite small. This has necessitated operating the tube in such manner that little or no grid current flows.

In our earlier applications we have disclosed and claimed a tube employing a generally tubular electrode intermediate the cathode and anode which can be at a positive potential relative to the cathode, the electrons emitted by the cathode being prevented from reaching or striking this electrode by an axial magnetic field. Moreover, by applying a modulating potential to this electrode it is possible to control or modulate the flow of electrons to the anode and therefore modulate the anode current and in effect, achieve amplification of an input signal applied between this control electrode and the cathode.

We have now found quite unexpectedly that the current density of the electron beam emitted by the cathode is very non-uniform. That is to say, at or near the edge current densities have been found to be up to one hundred times as high as found at or near the center of the cathode.

Based on this discovery we have found that certain geometrical configurations of the tube elements, especially in combination with one another, are preferred and even essential to construct a high performance power amplifier tube.

In order to illustrate the principles of the invention and to describe the invention in greater detail, reference is made to the accompanying drawing in which:

FIGURE 1 is a schematic representation of a tube according to the invention;

FIGURE 2a through 2h inclusive, show various forms of the cathode;

FIGURES 3a, b, c, and d, show additional cathode shapes in combination with the control electrode;

FIGURE 4 shows the angle of inclination of the anode surface struck b the electron beam;

FIGURE 5 shows the geometry of the control electrode;

FIGURE 6a shows in cross-section an elevational view 3,366,823 Patented Jan. 30, 1968 of a tube according to the invention, and FIGURE 6b shows a plan view in cross-section of the same tube.

The tube shown in FIG. 1 and as described in the earlier application as well, has three electrodes, an emitter 1 which is comparable with the cathode of an conventional electron discharge tube, a gate 2, comparable with the grid or control electrode of a triode, and collector 3, comparable to the anode of a triode.

The gate 2 is spaced axially a distance g from the emitter 1, and a distance e from the collector 3. The collector is also spaced transversely a distance 1 from the emitter. These distances, as will appear hereinafter, influence the operation of the tube.

Because an axial magnetic field will be applied between the emitter and collector, it has been found highly preferable to employ an indirectly heated emitter with an internally located heating element to avoid disturbing movements of the emitter. Thus, electromagnetic forces between the filament heating current (if a filamentary emitter were employed) and the magnetic field would tend to displace, dislocate or deform the filament either permanently (if DC current were used) or periodically with time (if AC current were used).

Since we have discovered that the beam current is concentrated adjacent to the edge of the emitter, it follows that an emitter having a large periphery for a given area is desirable. A minimum area is determined, of course, by the total beam current density which is limited by the emitter surface area, and nature of the emitter. Thus, FIGURES 2a through 211 show planar emitters having various peripheries for a given area.

In all cases the contour of gate 2 will conform to, or follow the shape of emitter 1 in such a way that the distance 1 between the edge of the emitter and the projection of the inner gate surface on the plane of the emitter is constant. Similarly, g is the distance between the lower edge of the gate and the emitter plane. Empirically we have found that both 1 and g influence the magnitude of the variations in gate potential necessary to modulate the beam intensity to the desired degree. Thus, we have found that a small f requires a low gate potential variation; but a small 1 also enhances the nonuniformity of the current drawn from the emitter. However, too great a non-uniformity reduces the useful life of the emitter by overloading certain areas while not effectively utilizing other areas nearer the center.

Extensive experiments have shown that for the best compromise between emitter life and low gate potential variation, should be larger than one-tenth of the width of the emitter, measured in a direction perpendicular to the surface of the gate.

For maximum modulability of the beam intensity, dimension g should not exceed dimension 1.

Instead of a flat, or planar emitter, convex emitters also can be used with good results.

Some examples of the latter are shown in FIGURES 3a, b, c and d. In FIGURE 3a, emitter 1 is the form of a square whose sides are inclined with respect to the axis of the gate. In FIGURE 3b, we have shown a circular emitter, while in FIGURE 30, we have shown an elliptical emitter and in FIGURE 3d, a rectangular emitter.

It must also be observed that the requirements as to the dimensions and g also apply as well to these configurations. Width of the emitter must now be considered as the thickness measured in a direction perpendicular to the gate surface.

Another important discovery found experimentally is that at a low collector potential electrons are repelled by the collector and returned to the emitter reducing the space potential in the vicinity of the emitter. The lower space potential reduces the magnitude of the current emitted. The resulting loss in current can be considerable, for instance, fifty percent or more of the original beam current.

Deflection of the returning electrons towards areas closer to the center of the cathode minimizes this effect. The space potential is still lowered, but at an area where the contribution to the total beam current is already rather low. The remaining loss in current is therefore less noticeable.

Deflection of reflected electrons can be achieved by giving the collector at the points of impact a shape such that the angle a between the collector surface and the incident electrons is less than 90 as shown in FIGURE 4. Empirically we have found that good results were obtained when this angle did not exceed 85, although at higher angles below 90, itis probable that reasonably good results could also be obtained.

The actual shape of the collector is relatively unimportant; what is material, is the angle at the points of impact. This requirement can be described, as follows:

Straight lines, parallel to the direction of the magnetic field and extending from the edge of the emitter, should form an angle a with the collector at the point of intersection less than 85.

Another factor influencing the performance of the tube as a power amplifier is the ratio between the height h of the gate and its width w (PEG. 5).

For good and flexible performance under conditions of varying load impedance the collector potential should be able to influence the electric field at emitter surface. However, the collector field should not have too great an influence on this electric field and the degree to which the collector field penetrates depends upon the ratio of the gate height-to-width. As shown in FIGURE 5, best results were obtained for A tube constructed in accordance with these principles described above is shown in FIGURES 6a and 6b, which are elevational and plan views of the tube in crosssection respectively. In this construction the copper collector 3 serves simultaneously as the vacuum envelope and is cooled by water flowing through channels 4. Emitter 1 is a rectangular flat emitter, heated by an internal filament 5, both sides of which are coated with a nickel matrix 6 impregnated with a mixture of bariumstrontiurn and calcium carbonates. The emitter is flanked by two flat metal plates 7 which serve as the gate. A magnet 8 is mounted around the tube to guide the electrons parallel to the gate plates.

While we have described the invention with reference to specific embodiments and applications thereof, other modifications will be apparent to those skilled in this art without departing from the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. An electron discharge tube comprising a planar emitter, an annular collector spaced from and surrounding said emitter, a gate extending between and spaced from the emitter and collector without appreciably intercepting electrons flowing between the emitter and collector, means to produce an axial magnetic field between the collector and the emitter to constrain electrons from impinging upon the gate, said emitter having a periphery which for a given emitter surface area is relatively large, said gate being spaced from the emitter in a plane parallel to the surface thereof a distance 1 which is larger than onetenth of the width of the emitter and is spaced from the surface of the emitter in a direction perpendicular to said surface a distance not exceeding said distance 1, said collector having a surface which forms an angle with electrons incident thereon of less than 90.

2. An electron discharge tube as claimed in claim 1, in which the collector forms an angle of less than with electrons incident thereon.

3. An electron discharge tube as claimed in claim 1, in which the emitter is indirectly heated.

4. An electron discharge tube as claimed in claim 3, in which the emitter is provided with an internally located filament element.

5. An electron discharge tube as claimed in claim 1, in which the emitter is rectangular.

6. An electron discharge tube as claimed in claim 1, in which the gate has a height h and a width w, and the ratio h/w exceeds 0.5 and is less than 2.

'7. An electron discharge tube as claimed in claim 5, in which the gate comprises two fiat plates flanking the emitter.

8. An electron discharge tube as claimed in claim 7, in which the collector constitutes a portion of the envelope of the tube.

9. An electron discharge tube as claimed in claim 8, in which the means for producing an axial magnetic field is a permanent magnet mounted around the collector.

References Cited UNITED STATES PATENTS 2,748,307 5/1956 Hickey 313-246 X 2,762,944 9/1956 Clogston 313162 X 2,953,706 9/1960 Gallet et a1. 3l3l62 X 3,175,120 3/1965 Wendt 3l3-84 X JAMES W. LAWRENCE, Primary Examiner.

S. A. SCHNEEBERGER, Assistant Examiner. 

